Effective Length
For antennas which are not defined by a physical area, such as monopoles and dipoles consisting of thin rod conductors, the aperture bears no obvious relation to the size or area of the antenna. An alternate measure of antenna gain that has a greater relationship to the physical structure of such antennas is effective length leff measured in metres, which is defined for a receiving antenna as:
where
- V0 is the open circuit voltage appearing across the antenna's terminals
- Es is the electric field strength of the radio signal, in volts per metre, at the antenna.
The longer the effective length the more voltage and therefore the more power the antenna will receive. Note, however, that an antenna's gain or Aeff increases according to the square of leff, and that this proportionality also involves the antenna's radiation resistance. Therefore this measure is of more theoretical than practical value and is not, by itself, a useful figure of merit relating to an antenna's directivity.
Read more about this topic: Antenna Aperture
Famous quotes containing the words effective and/or length:
“Before anything else [Numa] decided that he must instill in his subjects the fear of the gods, this being the most effective measure with an ignorant, and at that time uncultured, people.”
—Titus Livius (Livy)
“At length he would call to let us know where he was waiting for us with his canoe, when, on account of the windings of the stream, we did not know where the shore was, but he did not call often enough, forgetting that we were not Indians.... This was not because he was unaccommodating, but a proof of superior manners. Indians like to get along with the least possible communication and ado. He was really paying us a great compliment all the while, thinking that we preferred a hint to a kick.”
—Henry David Thoreau (1817–1862)